WASHINGTON/MONTREAL (Reuters) - Canada’s Bombardier Inc (BBDb.TO) expects to complete the final certification testing of its smaller new CSeries narrow-body commercial jet by the week of Nov. 23, a key milestone toward the plane being certified, four sources briefed on the plan said.

Fred Cromer, President of Bombardier Commercial Aircraft attends a news conference to present Swiss airline's new Bombardier CS100 passenger jet at Zurich airport near the town of Kloten June 18, 2015. REUTERS/Arnd Wiegmann

The Montreal-based manufacturer declined on Thursday to confirm the testing schedule, but said it still expects certification of the 110-seater CS100 by year’s end, followed by the jet’s entry into service in the first half of 2016.

The progress of the CSeries is being closely watched after years of delays and cost overruns on the program.

Three of the sources, who were not authorized to speak publicly about the matter, questioned whether the previously unreported November timetable could cause the plane and rail-maker to miss its year-end certification goal because of the tight schedule caused by the holiday season.

“Overall, things are looking positive for certification. Any delay will be more administrative than any sign of major issues,” said one of the sources. “As long as no significant technical issues come up, it should be just a few days into the next year.”

A second source said certification is still possible by year’s end, but everything would have to go perfectly in the certification process, which was rare.

However, Toronto-based Bombardier spokeswoman Marianella Delabarrera said certification will be completed “by the end of the year.”

Bombardier’s share price has dropped sharply on concerns about demand for the new jets and rising cost of the $5.4 billion program, which has strained the company’s balance sheet.

Richard Aboulafia, analyst with the Virginia-based Teal Group, is forecasting that the jet will go into service in the second half of 2016 with about 10 orders likely next year.

Bombardier needed about $1 billion to complete certification of the new jet, but would need about $3 billion in additional funding to help reel in the sales it needs to make the CSeries a success in the highly competitive marketplace, he said.